Assisted circulation techniques are an outgrowth of extracorporeal pump oxygenated systems developed in the mid-1950's. These techniques have been applied to patients for temporary assisted circulation, and more recently, for permanent left ventricular assistance. Most of the experimental and clinical application of these assist devices are based on the principle of diastolic augmentation. This is a system of counterpulsation where an external energy source delivers a pulsatile wave into the central circulation during cardiac diastole, and relaxes during cardiac systole. This is done by timing with the patient's electrocardiogram or pressure wave form.
This allows the following:
1. The stroke volume per unit work of the left ventricle is increased. PA1 2. The diastolic perfusion pressure and ratio of mean diastolic pressure to mean systolic pressure is increased. PA1 3. Coronary flow increases preferentially with diastolic pressure since coronary vascular resistance is minimal during cardiac diastole. PA1 4. Coronary collateral flow to ischemic region of the myocardium is increased. PA1 5. The modification of pulse pressure distribution in the aorta favors the increase of flow to vital organs. PA1 1. Effective hemodynamic support for the failing left ventricle. PA1 2. Be designed so that intermittent as well as continuous use can be achieved. PA1 3. Be failure free over long periods. PA1 4. Have a size and shape that interfer minimally with other organs. PA1 5. Be constructed of biologically compatible materials. PA1 6. Be implanted with a tolerable surgical risk. PA1 7. Be controlled reliably under varying physiologic conditions. PA1 8. Have a portable power source to allow the patient free movement. PA1 9. The transcutaneous connector should be constructed in such a way to facilitate easy connection to the power source with minimal risk of infection. PA1 1. Implantation does not require use of extra-corporeal circulation. PA1 2. Materials used have all been demonstrated to be biocompatible and certified for non-experimental or frequent clinical human use. PA1 3. It is felt the major risk of any permanent left ventricular assist device is ascending infection through the transcutaneous connector.
This principle has been applied since the mid-1960's as a temporary form of cardiac assistance for patients in acute heart failure with a commercially available intra-aortic balloon pump.
A permanent booster heart, based on the principles described above should have the following features:
Some attempts at implantation of a permanent left ventricular assist device over the past 10-12 years have met with limited success. The pioneer in this field is, Dr. Adrian Kantrowitz, who implanted (in 1965 and 1966) a mechanical U-shaped auxiliary ventricle in two patients. Problems occurred with synchronization and clotting in these patients. In 1970 through 1972, again under Dr. Adrian Kantrowitz, Dr. Steven Phillips did some definitive experimental work with the hemodynamic effects of a dynamic aortic patch in animals and, with Kantrowitz, implanted two such devices in patients. One patient did not survive the surgery. The second survived but died of infection a few months later that occurred via the transcutaneous connector. A third attempt in 1976 by Dr. Kantrowitz to implant another device was only successful short-term as the patient also died of ascending infection from the transcutaneous connector.
These above devices of Kantrowitz were implanted with utilization of the heart-lung machine and were based on the principle of diastolic augmentation. A transcutaneous connector required a skin button that ultimately caused the patients demise due to ascending infection.